feat: add support for ingress backed GlooEdge Gateway

Author: cucxabong

docs/annotations/annotations.md

@@ -150,14 +150,14 @@ If the annotation is not present, use the domains from both the spec and annotat
 
 ## external-dns.alpha.kubernetes.io/ingress
 
-This annotation allows ExternalDNS to work with Istio Gateways that don't have a public IP.
+This annotation allows ExternalDNS to work with Istio/GlooEdge Gateways that don't have a public IP.
 
-It can be used to address a specific architectural pattern, when a Kubernetes Ingress directs all public traffic to the Istio Gateway:
+It can be used to address a specific architectural pattern, when a Kubernetes Ingress directs all public traffic to the Istio/GlooEdge Gateway:
 
 - **The Challenge**: By default, ExternalDNS sources the public IP address for a DNS record from a Service of type LoadBalancer.
-However, in some service mesh setups, the Istio Gateway's Service is of type ClusterIP, with all public traffic routed to it via a separate Kubernetes Ingress object. This setup leaves the Gateway without a public IP that ExternalDNS can discover.
+However, in some setups, the Gateway's Service is of type ClusterIP, with all public traffic routed to it via a separate Kubernetes Ingress object. This setup leaves the Gateway without a public IP that ExternalDNS can discover.
 
-- **The Solution**: The annotation on the Istio Gateway tells ExternalDNS to ignore the Gateway's Service IP. Instead, it directs ExternalDNS to a specified Ingress resource to find the target LoadBalancer IP address.
+- **The Solution**: The annotation on the Istio/GlooEdge Gateway tells ExternalDNS to ignore the Gateway's Service IP. Instead, it directs ExternalDNS to a specified Ingress resource to find the target LoadBalancer IP address.
 
 ## external-dns.alpha.kubernetes.io/internal-hostname
 

docs/sources/gloo-proxy.md

@@ -104,3 +104,52 @@ spec:
         - --registry=txt
         - --txt-owner-id=my-identifier
 ```
+
+## Gateway Annotation
+
+To support setups where an Ingress resource is used provision an external LB you can add the following annotation to your Gateway
+
+**Note:** The Ingress namespace can be omitted if its in the same namespace as the gateway
+
+```bash
+$ cat <<EOF | kubectl apply -f -
+apiVersion: gloo.solo.io/v1
+kind: Proxy
+metadata:
+  labels:
+    created_by: gloo-gateway
+  name: gateway-proxy
+  namespace: gloo-system
+spec:
+  listeners:
+  - bindAddress: '::'
+    metadataStatic:
+      sources:
+      - resourceKind: '*v1.Gateway'
+        resourceRef:
+          name: gateway-proxy
+          namespace: gloo-system
+---
+apiVersion: gateway.solo.io/v1
+kind: Gateway
+metadata:
+  annotations:
+    external-dns.alpha.kubernetes.io/ingress: "$ingressNamespace/$ingressName"
+  labels:
+    app: gloo
+  name: gateway-proxy
+  namespace: gloo-system
+spec: {}
+---
+apiVersion: networking.k8s.io/v1
+kind: Ingress
+metadata:
+  labels:
+    gateway-proxy-id: gateway-proxy
+    gloo: gateway-proxy
+  name: gateway-proxy
+  namespace: gloo-system
+spec:
+  ingressClassName: alb
+EOF
+```

source/gloo_proxy.go

@@ -33,6 +33,10 @@ import (
 	"sigs.k8s.io/external-dns/source/annotations"
 )
 
+// GlooGatewayIngressSource is the annotation used to determine if the gateway is implemented by an Ingress object
+// instead of a standard LoadBalancer service type
+const GlooGatewayIngressSource = annotations.Ingress
+
 var (
 	proxyGVR = schema.GroupVersionResource{
 		Group:    "gloo.solo.io",
@@ -44,6 +48,11 @@ var (
 		Version:  "v1",
 		Resource: "virtualservices",
 	}
+	gatewayGVR = schema.GroupVersionResource{
+		Group:    "gateway.solo.io",
+		Version:  "v1",
+		Resource: "gateways",
+	}
 )
 
 // Basic redefinition of "Proxy" CRD : https://github.com/solo-io/gloo/blob/v1.4.6/projects/gloo/pkg/api/v1/proxy.pb.go
@@ -58,7 +67,22 @@ type proxySpec struct {
 }
 
 type proxySpecListener struct {
-	HTTPListener proxySpecHTTPListener `json:"httpListener,omitempty"`
+	HTTPListener   proxySpecHTTPListener `json:"httpListener,omitempty"`
+	MetadataStatic proxyMetadataStatic   `json:"metadataStatic,omitempty"`
+}
+
+type proxyMetadataStatic struct {
+	Source []proxyMetadataStaticSource `json:"sources,omitempty"`
+}
+
+type proxyMetadataStaticSource struct {
+	ResourceKind string                               `json:"resourceKind,omitempty"`
+	ResourceRef  proxyMetadataStaticSourceResourceRef `json:"resourceRef,omitempty"`
+}
+
+type proxyMetadataStaticSourceResourceRef struct {
+	Name      string `json:"name,omitempty"`
+	Namespace string `json:"namespace,omitempty"`
 }
 
 type proxySpecHTTPListener struct {
@@ -136,6 +160,14 @@ func (gs *glooSource) Endpoints(ctx context.Context) ([]*endpoint.Endpoint, erro
 			log.Debugf("Gloo: Find %s proxy", proxy.Metadata.Name)
 
 			proxyTargets := annotations.TargetsFromTargetAnnotation(proxy.Metadata.Annotations)
+			if len(proxyTargets) == 0 {
+				proxyTargets, err = gs.targetsFromGatewayIngress(ctx, &proxy)
+				if err != nil {
+					log.Error(err)
+					return nil, err
+				}
+			}
+
 			if len(proxyTargets) == 0 {
 				proxyTargets, err = gs.proxyTargets(ctx, proxy.Metadata.Name, ns)
 				if err != nil {
@@ -228,6 +260,48 @@ func (gs *glooSource) proxyTargets(ctx context.Context, name string, namespace s
 	return targets, nil
 }
 
+func (gs *glooSource) targetsFromGatewayIngress(ctx context.Context, proxy *proxy) (endpoint.Targets, error) {
+	targets := make(endpoint.Targets, 0)
+
+	for _, listener := range proxy.Spec.Listeners {
+		for _, source := range listener.MetadataStatic.Source {
+			if source.ResourceKind != "*v1.Gateway" {
+				log.Debugf("Unsupported listener source. Expecting '*v1.Gateway', got (%s)", source.ResourceKind)
+				continue
+			}
+			gateway, err := gs.dynamicKubeClient.Resource(gatewayGVR).Namespace(source.ResourceRef.Namespace).Get(ctx, source.ResourceRef.Name, metav1.GetOptions{})
+			if err != nil {
+				return nil, err
+			}
+			ingressStr, ok := gateway.GetAnnotations()[GlooGatewayIngressSource]
+			if ok && ingressStr != "" {
+				namespace, name, err := ParseIngress(ingressStr)
+				if err != nil {
+					return nil, fmt.Errorf("failed to parse Ingress annotation on Gateway (%s/%s): %w", gateway.GetNamespace(), gateway.GetName(), err)
+				}
+				if namespace == "" {
+					namespace = gateway.GetNamespace()
+				}
+
+				ingress, err := gs.kubeClient.NetworkingV1().Ingresses(namespace).Get(ctx, name, metav1.GetOptions{})
+				if err != nil {
+					log.Error(err)
+					return nil, err
+				}
+
+				for _, lb := range ingress.Status.LoadBalancer.Ingress {
+					if lb.IP != "" {
+						targets = append(targets, lb.IP)
+					} else if lb.Hostname != "" {
+						targets = append(targets, lb.Hostname)
+					}
+				}
+			}
+		}
+	}
+	return targets, nil
+}
+
 func sourceKind(kind string) *schema.GroupVersionResource {
 	if kind == "*v1.VirtualService" {
 		return &virtualServiceGVR